It is typical in the paper, film and foil industries to first form a wide web of material which is later cut into smaller, individual rolls or packets. The web, typically provided as a roll, passes continuously over the knife edge of a plurality of spaced apart slitters. The slitters slit the web into a plurality of individual rolls that are wound on separate take-up rollers for packaging and shipping.
A bottom slitter or anvil is typically used in conjunction with a circular top slitter having a sharp cutting edge. The bottom slitter typically is a cylinder having a marginal wall section that is tapered inwardly at an angle of about three degrees to provide a knife edge. The cutting edge of the top slitter contacts the knife edge of the bottom slitter. The bottom slitter rotates on a shaft in one direction while the top knife is rotated in the opposite direction. The web is thereby cut as it passes between the top and bottom slitters.
A bottom slitter is typically manufactured either as a single unitary piece, or as two halves or semi-circular members. Slitters made from two halves are known in the industry as a split slitters or bands. In the case of a split slitter, each half is placed on a drive shaft and the mating ends or surfaces are aligned with each other. The two semi-circular members are then rigidly connected to each other using conventional fasteners.
Achieving proper alignment between the two halves is very important. A small misalignment between the two halves can result in a mis-matched cutting edge resulting in a chipped top slitter blade. Misalignment can also disturb the direction of the cut and/or can result in frayed edges. To insure proper performance, the two slitter halves must fit together and be precision aligned in both the radial direction and in the axial direction. To achieve this precision, the mating ends of the two halves are typically precision machined to tight tolerances. For example, typically the mating ends of the slitter members must fit together in both the axial and radial directions within a tolerance range of from zero clearance to 0.0002 inches.
As mentioned, the two semi-circular halves of prior art slitters typically have precision machined mating ends These mating ends typically incorporate some form of tongue and groove arrangement (e.g., male and female keyways) to provide the precision alignment between the two slitter halves. For example, many prior art slitters utilize complicated lands or projections on the mating surface of one halve that are received in complicated recesses or pockets in the matting surface of the other halve. Because they are complicated structures with many surfaces and corners, these prior art lands and recesses require substantial machining time and are expensive to manufacture.
U.S. Pat. Nos. 5,085,535 and 5,531,536, for example, each disclose a mating arrangement that includes a multi-level land and a complimentary multi-level recess disposed to receive the multi-level land. Insertion of the multi-level land into the multi-level recess during engagement of the two slitter halves insures that the desired axial and radial alignment will be achieved.
The mating arrangement disclosed in U.S. Pat. No. 5,085,535, which issued on Feb. 4, 1992 to Solberg et al. and is incorporated by referenced herein, includes a multi-level recess on one of the mating ends. The deepest of the recesses, which provides for axial alignment of the two slitter halves, extends through the entire radial width of the mating end. In other words, the deepest recess is not centrally disposed on the mating surface in which it projects, but rather extends all the way to the outside surfaces of the slitter. The tallest portion of the multilevel land received in this recess, however, does not extend the entire radial width of the split slitter, but rather is centrally disposed inward from the outer radial edges (and surfaces) of the mating end and therefore does not completely fill the recess. As a result, the two ends of the recess used for axial alignment open up to the outer and inner radial surfaces of the slitter. This results in an exposed open slot being present on the outer and inner radial surfaces of the slitter.
Similarly, the arrangement disclosed in U.S. Pat. No. 5,531,536, which issued on Jul. 2, 1996, to Blanchfield et al., and which is also incorporated by referenced herein, also includes a multi-level recess. The deepest of the recesses, which provides for radial alignment of the two slitter halves, extends through the entire axial width of the mating end. The tallest portion of the multilevel land that is received in this recess, however, also does not extend the entire axial width of the slitter, but rather is centrally disposed inward from the outer axial edges (and surfaces) of the mating end. As a result, the two ends of the recess used for axial alignment open up to the outer and inner axial surfaces of the slitter, thus forming an exposed open slot on each of outer axial surfaces of the slitter.
The slots formed on the outer slitter surfaces by the open recesses can be problematic. Any burrs that are present around the recess openings will have a tendency to collect dust and paper fibers as the web passes over the slitter. This can be especially problematic with respect to the opening that appears on the outer radial surface of the slitter because the web rides on that surface. As the paper fibers collect, they form a ball that can place a dent in the web as the web passes over the slitter.
To alleviate the potential for such dust and paper fiber collection, the recess openings are typically deburred during manufacturing of the slitter. The deburring process, however, is time consuming and labor intensive for it typically is performed by hand filing. It is therefore desirable to have a slitter and mating arrangement that does not have any keying or recess openings on the outside surfaces of the slitter. Preferably, the male and female keys (e.g, lands and recesses) will be completely enclosed or hidden inside of the slitter when the two halves are mated together.
The prior art keying arrangements disclosed in U.S. Pat. Nos. 5,085,535 and 5,531,536 also require a significant amount of time to precision machine. This is because each mating end includes three surface levels (e.g, a mating surface and a two level land or recess). Each of these surface levels is typically first rough cut and then precision cut. As a result, a total of six machining operations or passes are required to precision machine these keying arrangements. It is desirable to have a mating arrangement that requires less machining time to manufacture. Preferably, the mating arrangement will have no more than two surface levels (e.g, a mating surface and a single-level land or recess).
Another problem with the prior art slitters disclosed in U.S. Pat. Nos. 5,085,535 and 5,531,536 relates to the numerous right angle (e.g., square) corners that are prevalent on each mating end between the various keying elements. The square corners increase the likelihood that stress cracking will occur during heat treating of the slitter. Cracked slitters must be scrapped. The square corners are also susceptible to being damaged during repeated assembly and disassembly of the two slitter halves. It is desirable therefore to provide a mating arrangement that minimizes the number of square corners that are present. Preferably, the corners and edges of the keying elements will be chamfered or beveled to minimize the likelihood of cracking and to provide a lead-in taper during assembly of the slitter halves.
The presence of square corners along the top edge of the lands and along the top edges of the recesses can also become problematic if the cutting tools used for machining the recesses become worn. This is because a worn cutting tool will inevitably result in an undesirable radius forming in the recess corners formed between the recess sidewalls and the bottom surface of the recess. An undesirable radius can also form between the land sidewalls and the mating surface from which they project. These undesirable radii can interfere with square corners along the top edge of the land or along the top edge of the recess, essentially blocking the land from fully seating in the recess when the land is received in the recess. It is desirable, therefore to chamfer or bevel the top edges of the lands and the top edges of the recess to provide clearance between the top land edge and the bottom corners of the recess and between the top recess edge and the corners located at the bottom of the land sidewalls.
A prior art method from a different art that is used for aligning two parts in both the radial and axial direction involves the use of cylindrical (round) machined dowel pins and drilled holes. This method for aligning two parts, however, does not provide the desired level of precision that is necessary for split slitters and other similar devices that require tight tolerancing. This is because of the clearance requirements that are necessary in order for the machined dowel pin to be received in the drilled hole. These clearance tolerances fall outside of the tolerancing limits that are required to maintain the precision alignment between the two halves of split slitters. As a result, machined dowel pins and drilled holes cannot be used to provide the axial and radial alignment that is needed for the construction of properly aligned split slitters.